This invention relates to an improved apparatus and method for weighing a plurality of articles of varying weights and for delivering a collection of the weighed articles having a combined weight which is at least equal to and which most nearly approximates a predetermined target weight.
In today's competitive environment, food processors and manufacturers are packaging food commodities such as candies, nuts, pasta and the like in conveniently sized packages. In such packaging, it is important to ensure that each package contains at least the stated weight. It is also important to the packagers to minimize any overweight packages since any excess weight, over the stated minimum, represents a serious loss of profit. In a competitive environment, it is also important to operate the weighing and packaging machines at a relatively rapid rate so that the overall costs of packaging and product are minimized.
Over the past decade or so, manufacturers and packagers have advanced the art of rapid packaging, particularly with respect to combination weighers and packaging machines. For example, the U.S. patent of Gordon W. Hays, U.S. Pat. No. 4,313,507, which issued on Feb. 2, 1982, discloses a combination weigher which consistently arrives at a weight portion within an acceptable range. Hays recognized that the number of immediately available articles (ready articles) will usually be significantly greater than the number of average weight articles needed per portion. Hays then selected a combination of ready articles the total weight of which equals or most minimally exceeds the final desired weight of the portion.
Another approach for obtaining a precise weight of a product formed of a plurality of individual articles having various weights is disclosed in U.S. Pat. No. 3,939,928 of Katsuhiko Murakami et al. which issued on Feb. 24, 1976. As disclosed therein, a number of objects are fed to a plurality of weighing hoppers and an electronic circuit is used to test successive combination of hoppers for a combined weight which is equal or most closely approximate to a preselected target weight. The selected hoppers are then unloaded.
Since the number of weighing balances normally selected is a less than the number of remaining ones, it is customary to superpose cycles, which is referred to as interleaving, in order to increase the speed and efficiency of the process. Interleaving is a widely-used method for increasing the speed in multi-scale devices. For example, in 1979 Parson Automatic Scale Company of Berkeley, Calif., now part of The Paxall Group of Skokie, Ill., manufactured a multi-scale unit which incorporated interleaving or overlapped cycles to increase the speed of the weighing process. In that unit, four weigh heads were incorporated. In a first cycle, two heads, each of which weighed a fraction of a total charge, were discharged into a single package. Then, before those two heads were refilled, the third and fourth units, each of which contained a part of a second charge, were discharged into a second package. In essence, the first two scales were excluded from the second selection.
A more detailed description of interleaving is contained in the U.S. patents of Hirano, U.S. Pat. Nos. 4,385,671, 4,470,166 and 4,589,506. The systems defined therein exclude a group of scales which were selected in an initial combination search from a second combination search. While this system allows for an increase in speed, it may not result in an optimum, i.e., most accurate weight of product which is delivered to a package. The reason is that once an initial search has been selected, that selection is fixed and will be discharged into the next available package while a second combination search, which excludes the previous selected group of scales, is initiated.
Accordingly, it now appears that there may be a significant demand for a dynamic method and apparatus for controlling interleaving based on internal parameters and/or external operating parameters. Such apparatus and method would be based on considerations of "ready" scales, i.e., those scales which have been refilled and/or reached a steady state. For example, such apparatus and/or method would consider any and all individual scale(s) which becomes ready after the initial selection process at the time of discharge as opposed to excluding a group or set of previously selected scales. An example of an apparatus which incorporates "ready" or stable scales is disclosed in the U.S. Pat. No. 4,733,363 of Yamada et al. which is incorporated herein in its entirety by reference.
It has now been found that a combination weigher according to the present invention can be used to improve the machine efficiency and desired weight accuracy by means of novel control means for optimizing performance at various production rates. It has also been found that the apparatus and methods according to the present invention provide maximum versatility wherein a combination weigher can accomodate discharge weights or values of very light density products that require a relatively large number of balances to make up a required weight. It is also believed that the combination weigher in accordance with the present invention can be manufactured at a competitive price, readily maintained and efficiently operated and will not add to the demands of the operator. In addition, a weigher in accordance with the present invention can operate over a relatively large range of speeds and target weights with minimal operator input.